Method for controlling a multiphase interleaving converter and corresponding controller

ABSTRACT

A method is provided for controlling a converter of the multiphase interleaving type. According to the method, there is detected when a change of the load applied to an output terminal of the converter occurs. All the phases of the converter are simultaneously turned off, and a driving interleaving phase shift is recovered so as to restart a normal operation of the converter. A controller for carrying out such a method is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 13/089,802,filed Apr. 19, 2011, now U.S. Pat. No. ______, which is a divisional ofapplication Ser. No. 11/680,581, filed Feb. 28, 2007, now U.S. Pat. No.7,956,590. The entire disclosures of prior application Ser. No.13/089,802 and prior application Ser. No. 11/680,581 are hereinincorporated by reference. Additionally, this application claimspriority from European Patent Application No. 06 425 132.5, filed Feb.28, 2006, European Patent Application No. 06 425 133.3, filed Feb. 28,2006, and European Patent Application No. 06 425 131.7, filed Feb. 28,2006. The entire disclosures of these three European patent applicationsare herein incorporated by reference. Further, this application isrelated to the applications “METHOD FOR CONTROLLING A MULTIPHASEINTERLEAVING CONVERTER AND CORRESPONDING CONTROLLER,” Attorney DocketNo. 220-P0061, Ser. No. 11/680,250, now U.S. Pat. No. 7,885,088, and“METHOD FOR CONTROLLING A MULTIPHASE INTERLEAVING CONVERTER ANDCORRESPONDING CONTROLLER,” Attorney Docket No. 220-P0063, Ser. No.11/680,586, now abandoned, which were filed on the same day as priorapplication Ser. No. 11/680,581 and commonly assigned toSTMicroelectronics S.r.l. These related applications are hereinincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a method for controlling a multiphaseinterleaving converter and a corresponding controller, and moreparticularly relates to a method for controlling a converter of themultiphase interleaving type when an associated load connected to it issuddenly released.

BACKGROUND OF THE INVENTION

As is known, the evolution of the electrical features of the processorsfor PCs, workstations and servers obliges manufacturers to find newsolutions to meet the requirements demanded by central processing units(or CPUs).

In particular, CPUs of the new generation require high precision intheir supply voltage, equal for example to +/−0.8% in the steady stateand +/−3% in the transient state.

Next to these requirements for precision, the supply voltages that areused decrease to 1.1V and the load currents rise to 130 A with edges of100 A/μs, with a requirement for efficiency higher than 80%.

Therefore, suitable current or voltage controller devices must be used,which are able to ensure the efficiency required. A controller devicesuitable for CPU applications comprises for example a converter of theDC-DC interleaving type, used as an economic and efficient solution tomeet the above needs and obtained by connecting, in parallel, N DC-DCconverters in a Buck or Step-down configuration (i.e., by connectingtheir input and output terminals to each other driven in interleavedmode).

A known converter of the DC-DC interleaving type is shown in FIG. 1A.The converter 1 comprises a controller 2 connected to a plurality of nbuffers or phases 3 (multiphase configuration) essentially comprisingpairs of switches (High Side and Low Side), driven by the controller 2so as to supply the required power to a CPU 4, which is connected to theoutput terminal OUT of the converter 1.

The interleaving driving of the converter 1 also implies that thecontroller 2 turns on the High Side switches of the n phases with aphase shift equal to the switch period T divided by the number n ofphases.

A multiphase interleaving converter 1 is shown in greater detail in FIG.1B. In particular, the converter 1 comprises n phases (indicated in thefigure by their inductors L1 to Ln), with each phase 3 comprising a HighSide switch SWhs connected in series to a Low Side switch SWIs between afirst and a second voltage reference, in particular an input voltage Vinand ground GND.

Each phase 3 also comprises an inductor L connected to a switch node X,or phase node that is between the switches SWhs and SWIs. The converter1 also comprises an output capacitor Cout inserted between the outputterminal OUT and ground GND. Across the capacitor Cout there is anoutput voltage value Vout which is applied to the CPU 4.

The controller 2 supplies a driving signal of the PWM type for the HighSide SWhs and Low Side SWIs switches of the phases 3, which aresensitive to the level of the signal PWM. In particular, the High Sideswitches and the Low Side switches are respectively on and off if PWM=1,and the High Side switches and the Low Side switches are off and onrespectively if PWM=0. To achieve this, the controller 2 comprises asuitable modulator 5.

In recent years, processors have been required to have their currentspecifications summarized in the underlying type of table.

TABLE 1 2004A 2004B 2004C 2005A 2005B 2006A IMAX  78 A 119 A 112 A 100 A125 A 65 A ISTEP  55 A  95 A  89 A  65 A  95 A 40 A/60 A Istep/Trise  69A/ms 119 A/ms 111 A/ms 217 A/ms 317 A/ms 1200 A/ms IDCmin  5 A  5 A  5 A 5 A  5 A 5 A ITDC  68 A 101 A  96 A  85 A 115 A 56 A I_RISE 800 nsec800 nsec TBD/04_A 310 nsec 310 nsec 50 nsec

It should be noted that the increase in the required maximum currents(IMAX) stopped in 2005 and a decrease is foreseen in 2006 passing fromabout 125 A to 65 A. Such a decrease in the required maximum currentwould lead towards converter designs using a lower number of phases withrespect to the preceding years.

In parallel, a very strong increase in the current demand rate of theprocessors (Istep/Irise) occurs, which greatly complicates the design ofthe DC-DC interleaving converters: the rate value Istep/Irise passes infact from 69 A/ms (value in 2004) to the foreseen value of 1200 A/ms in2006.

In other words, DC-DC interleaving converters of the next generation arerequired to meet more and more sudden load changes (or Load Transients).This need is also present in the case of a fast releasing of a load.

All this implies an increase in the costs of these converters for whichthe number of output capacitors Cout and thus the number n of phases ofthe converter itself is to be increased to respect the required voltagetolerances.

In particular, if up to now the number n of phases has been selected onthe basis of efficiency, temperature of the components (i.e.,reliability) and power density requirements, in the following years thenumber of phases will be established also on the basis of the requiredcurrent speed specifications to be achieved.

Increasing the number of phases is in fact a way to increase theresponse speed of the converter to load requirements, in particular tosudden decreases of such requirements when the load is released.

Clearly, in the case of current changes equal to 70 A in a range of 50ns, only an adequate number of ceramic capacitors can limit the voltagefall of the processor in the first 50 ns of the load transient.

In fact, the regulator has a band, which is proportional to n×Fsw, withn being the number of phases of the converter and Fsw being theswitching frequency, in general about 300 kHz. Thus, there are obtainedresponse times which are in inversely proportional to the band (forexample, for n=4 a response time of about 800 ns is obtained).

The converter and its response speed can thus heavily influence itsmanufacturing cost and the number of electrolytic capacitors to be used(which influence the output voltage fall for the processor over longertimes than for the ceramic capacitors).

Further, the band and response speed of the converter are however twoindexes that no longer function for load transients as short as 50 ns,which cannot be considered a “small signal” shifting any more since thereaction times of the closed loop system (i.e., the band) are greater byat least one order of magnitude.

The known solutions aim at improving the response times of thecontroller without for this reason influencing its band.

An example of this known type of solution is shown in FIG. 2.

The controller 20 has a terminal OUT for its connection with a CPU,whereon there is a voltage signal Vout. The terminal OUT is connected toa first inner terminal FB by a resistor Rfb, and an error amplifier EAhas a first input terminal, in particular an inverting one, connected tothe first inner terminal FB as well as to a first current generatorGdroop for supplying this first input terminal of the error amplifier EAwith a voltage value Idroop equal to K*I_(TOT), with K being a suitablescale factor and I_(TOT) being a total current value flowing in theinductors of the phases of the converter to which the controller 20 isconnected.

The error amplifier EA has a second input terminal, in particular anon-inverting one, that receives a reference voltage Ref, as well as anoutput terminal connected to a second inner terminal COMP of thecontroller 20, which is, in turn, feedback connected to the first innerterminal FB by the series made of a resistor Rf and of a capacitor Cf.

The second inner terminal COMP is connected to a plurality of controlmodules 21, in parallel to each other, and each having an outputterminal 0 connected to a phase of the converter.

In particular, each control module 21 is inserted between a first and asecond voltage reference, in particular a supply voltage Vdd and groundGND, and is connected to the second inner terminal COMP.

A generic control module 21 comprises a resistor Rs and a capacitor Cs,which are inserted in parallel between the second inner terminal COMPand an inner node Y of the control module, which is, in turn, connectedto ground GND by a biasing generator Gp, which supplies a current valueequal to K*I_(L), where K is the scale factor and I_(L) is a value ofthe current flowing in the inductor L of the phase that is connected tothe control module 21.

The control module 21 also comprises an input generator Gi, which isinserted between the supply voltage reference Vdd and the inner node Y,and is suitable for supplying a current value equal to K*I_(AVG), whereK is the scale factor and I_(AVG) is a mean value of the currentsflowing in the inductors L of the phases of the converter.

The inner node Y is also connected to a first input terminal, inparticular a non-inverting one, of an operational amplifier OA of thecontrol module 21, which also has a second input terminal, in particularan inverting one, which receives a ramp signal RAMP (having frequencyFSW), and an output terminal O, which is connected to a correspondingphase of the converter and supplies this phase with a driving signalPWM.

To improve the response time of the controller 20 without modifying itsband, a supplemental capacitor Cd is inserted between the first innerterminal FB and the terminal OUT, in parallel to the resistor Rfb.

In this way, when there is a particularly quick Load Transient, thissupplemental capacitor Cd becomes a much smaller impedance than theresistor Rfb resulting in the voltage value at the first inner terminalFB being no longer latched at a value equal to the reference voltage Ref(virtual ground due to the gain of the error amplifier EA) but it isdragged by the voltage signal Vout at the terminal OUT of the controller20. The output terminal of the error amplifier EA, corresponding to thesecond inner terminal COMP, thus suddenly rises upwards with a speedproportional to the parameter GBWP (Gain Bandwidth Product) of the erroramplifier EA and it saturates beyond the height of the driving signalsPWM produced by the control modules 21.

In FIG. 2, the index j indicates the different phases of the converterconnected to the controller 20, which, as previously described, comprisea High Side switch SWhs, inserted between an input voltage Vin and aswitch node X (or phase node), and a Low Side switch SWIs, insertedbetween the phase node X and ground GND, as well as an inductor L,inserted between the phase node X and the terminal OUT of the converter1 whereon there is an output voltage value Vout, as well as a capacitorCout inserted between the terminal OUT and ground GND.

The driving signals PWM set the turn on and off times of the switchesSWhs and SWIs. In particular, when the driving signal PWM is at a highvalue, or “1”, then the High Side switch SWhs is closed and the Low Sideswitch SWIs is open. In a dual way, if the driving signal PWM is at alow value, or “0”, then the High Side switch SWhs is open and the LowSide switch SWIs is closed.

Thanks to the configuration of the controller 20 shown in FIG. 2, thecurrent I_(L) flowing in each inductor L of each phase of the converteris read by the controller 20 through the scale factor K.

Although advantageous under several aspects, this known solution showstwo important problems.

1) Even if the controller 20 realizes a sudden and quick movement of theinner terminal COMP (further to a Load Transient), each phase respondsin reality only marginally to this Load Transient and does notcompletely contribute to sustain the voltage value Vout required atoutput due to the presence of the interleaving phase shifts of thephases themselves.

2) The speed with which the inner terminal COMP moves (a function of theparameter GBWP of the error amplifier EA) influences the speed at whichthe phases driven by the controller 20 are turned on or turned on againfurther to a Load Transient.

The first problem can be immediately linked to the choice of the timeconstant of the controller 20, which is equal to Cd*Rfp where:

the value of the resistor Rfb is chosen so as to program a desired droopeffect, i.e., a departure of the voltage signal Vout from a value of thereference given by K*I_(TOT)*Rfb, with K being generally chosen so as todetermine a maximum possible value of supplied current; and

the value of the supplemental capacitor Cd is chosen as high as possibleso as to reduce the impedance of the parallel connection between itselfand the resistor Rfb in the case of a Load Transient.

However if the value of the supplemental capacitor Cd is too high, itsderivative action also occurs in the steady state, i.e., in the absenceof a Load

Transient, by substantially amplifying the ripple of the voltage Vout(which is a signal with a value equal to about 10 mV and recurring atfrequency n*Fsw, with n being the number of phases of the converter). Ifthis occurs, the converter becomes unstable.

In other words, for a correct operation of the controller 20 thefollowing relation is always to be respected.

½πRfb*Cd>n*Fsw

where Rd is the resistance value of the resistor Rd, Cd is thecapacitance value of the capacitor Cd, and n*Fsw is the frequency of thesignal Vout.

All this limits the movement of the inner terminal COMP for which eachphase with a driving signal PWM higher than a control voltage in theinstant when there is a Load Transient is only marginally turned on, asshown in FIG. 3.

In particular, this figure shows that the current of the inductor of thephase F4 is only marginally interested by the Load Transient, so onlythree phases out of four contribute to the rise of the output voltagevalue Vout. This situation is valid in a general way: only n−1 phasesrespond to a current change associated with a Load Transient, with atleast one phase remaining “lazy”.

The second problem is instead associated with the repeatability of theparameter GBWP of the error amplifier EA of the controller 20. It isknown that this parameter GBWP depends on a great number oftechnological parameters such as oxide thickness, lithographictolerances, diffusivity of dopants, etc. Apart from the variance withthe junction temperature, a departure of at least +/−50% from a nominalvalue of the parameter GBWP of an amplifier is a realistic situation.

Thus, considering an error amplifier EA with nominal GBWP of 30 MHz(which corresponds to a value of A0 equal to 100 dB and to a pole at 300Hz), practically, the value of the parameter GBWP could vary between 15MHz and 45 MHz.

By repeating the simulations on the known controller 20 with erroramplifiers EA having the two extreme values indicated above for theparameter GBWP, the patterns shown in FIGS. 4A and 4B, respectively, areobtained, which highlight the dependency of the change of the outputvoltage Vout on the real value of the parameter GBWP of the erroramplifier EA.

It thus occurs that, if for GBWP=45 MHz three phases out of four respondto the Load Transient, for GBWP=15 MHz, only two phases out of fourrespond to the same Load Transient. Thus the fall value of the outputvoltage Vout of the converter passes from 110 mV (with GBWP of 45 MHz)to 125 mV (with GBWP of 15 MHz).

Moreover, this known solution has no control during the load releasestep and is not able to “follow” sudden decreases of the currentrequirements under these release conditions with the production ofundesired overshoots of the output voltage value.

To try and solve this problem, a technique called “body-brake” has beenrecently proposed which is used in the case of the release of the loadand is described in U.S. Pat. No. 6,806,689. A method for controlling aconverter of the multiphase interleaving type using the body-braketechnique provides that under load release conditions, all the High Sideand Low Side switches are turned off (while traditionally, i.e., in thecase of controllers which do not use this body-brake technique, thecontroller would turn off the High Side switches but would turn on theLow Side switches SWIs).

In this way the overshoot of the output voltage Vout after the loadrelease is greatly decreased with respect to controllers which do notuse this body-brake technique. In fact, the excess of charge dQgenerated by the cancellation of the currents of the inductors L of themultiphase interleaving converter phases is decreased thanks to thepresence of Low Side switches that are off.

In particular, in the case in which traditional controllers are used,this charge excess is equal to the following.

dQ=L/Vout*Ipeak

Ipeak being a value of residual current in the inductances L of theconverter phases, the voltage fall across these inductors L is equal tothe output voltage Vout.

On the contrary, by using the body-brake technique, the voltage fallacross the inductors L is equal to Vout+Vdiode, with Vdiode being thevoltage value across the intrinsic diode of the Low Side switches underthe off condition.

Thus, the fall across the inductors L is decreased thanks to the voltagefall on these intrinsic diodes and the charge excess is given by thefollowing.

dQ=L/(Vout+Vdiode)*Ipeak.

Thanks to this decrease of the charge excess dQ, a decrease of theovershoot of the output voltage Vout is obtained.

The on and off conditions of the Low Side switches are shown in FIGS. 4Aand 4B, and the corresponding patterns of the current values in theinductors of the phases and the output voltage are qualitatively shownin FIGS. 4C-4E.

In particular, it is known to detect the load release condition bycomparing a control voltage Vcntr (corresponding to an output voltagevalue of the error amplifier EA, i.e., the voltage value COMP) with areference voltage Vr as well as with a clamping voltage Vclamp of thebody-brake.

Normally, the reference voltage Vr has a ramp or sawtooth periodicalwave form, as shown in FIG. 4E. The turn-on (ON) and the turn-off (OFF)of the High Side and Low Side switches is then decided according to thefollowing rules.

If Vctr>Vr then High Side ON and Low Side OFF;

if Vctr<Vr and Vcntr>Vclamp then High Side OFF and Low Side ON; and

if Vctr<Vr and Vcntr<Vclamp then High Side OFF and Low Side OFF, thislatter condition corresponding to the body-brake technique.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a control method,and a corresponding controller, for a converter of the multiphaseinterleaving type having such structural and functional characteristicsas to ensure that the output voltage value follows sudden loaddecreases, so as to overcome the limits and the drawbacks that affectknown converters.

Another object of the present invention is to provide a control method,and a corresponding controller, that force the multiphase interleavingconverter phases so that all respond to a load transient at the sametime, in particular under a release condition of the load, substantiallyinterrupting and recovering the interleaving driving mechanism.

One embodiment of the present invention provides a method forcontrolling a converter of the multiphase interleaving type. Accordingto the method, there is detected when a change of a load applied to anoutput terminal of the converter occurs. All phases of the converter aresimultaneously turned off, and a driving interleaving phase shift isrecovered so as to restart a normal operation of the converter.

Another embodiment of the present invention provides a controller for aconverter of the multiphase interleaving type. The controller includesat least one input terminal connected to an output terminal of theconverter, at least one output terminal connected to phases of theconverter, at least one load change detector applied to the outputterminal of the converter, and an output comparator. The outputcomparator has at least one input terminal receiving an inner signal ofthe converter, and an output terminal connected to the output terminalof the controller for generating a turn-off control signal for thephases of the converter. The turn-off control signal forces the turn-offof the phases of the converter.

Other objects, features, and advantages of the present invention willbecome apparent from the following detailed description. It should beunderstood, however, that the detailed description and specificexamples, while indicating preferred embodiments of the presentinvention, are given by way of illustration only and variousmodifications may naturally be performed without deviating from thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show a known converter of the multiphase interleavingtype;

FIG. 2 shows a known controller for a converter of the multiphaseinterleaving type;

FIGS. 3A-3C show the patterns of signals inside a known converter of themultiphase interleaving type under different operation conditions;

FIGS. 4A-4E show equivalent circuits and patterns of signals inside aknown converter of the multiphase interleaving type that uses thebody-brake technique;

FIG. 5 shows a controller for a converter of the multiphase interleavingtype according to one embodiment of the present invention;

FIG. 6 shows greater detail of a portion of the controller of FIG. 5;

FIG. 7 shows greater detail of the controller of FIG. 5 according to apreferred embodiment of the present invention;

FIGS. 8A-8C show the patterns of signals inside the controller of FIG.5; and

FIG. 9 shows an inner configuration of the controller of FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail hereinbelow with reference to the attached drawings.

The present invention starts from the consideration that the problems ofresponse to sudden load changes (or Load Transients) applied to aconverter of the multiphase interleaving type are mainly linked to theinterleaving driving mechanism which shifts the response of the singlephases of the converter; phase shift is an obstacle against a quickresponse of the converter itself. In particular, it has been consideredhow the ideal response to a Load Transient by the converter is that allthe phases respond at the same time and how exactly the interleavingphase shift adopted for the driving of the phases does not allow theirsimultaneous turn off.

Advantageously according to the present invention, a method is proposedfor controlling a converter of the multiphase interleaving type thatincludes the steps of:

1) detecting when a load change applied to an output terminal of theconverter (a Load Transient) occurs, in particular a release conditionof the load;

2) simultaneously turning off all the phases of the converter, inparticular zeroing the temporal phase shift of the interleaving driving;and

3) recovering the phase shift of this interleaving driving, so as torestart a normal operation of the converter.

In an illustrative embodiment, the step of detecting the Load Transientcomprises detecting the positive derivative of the voltage signal Voutat the output terminal of the converter and generating a detectionimpulse signal LTPULSE in correspondence with the detected LoadTransient.

Advantageously according to the illustrative embodiment of the presentinvention, in accordance with the technique which is known asbody-brake, the step of simultaneously turning off all the converterphases comprises simultaneously turning off all the power transistors ofthe phases.

In substance, the step of turning off the phases forces the conditionsin which the High Side switches of the phases are OFF, and, contrary tothe known converters, the Low Side switches of the phases are also OFF.

In a preferred embodiment, the control method according to the presentinvention also comprises a regulation step of this detection impulsesignal LTPULSE.

Moreover, in the illustrative embodiment the step of simultaneouslyturning off all the phases of the converter comprises generating aturn-off control signal LowsideOff that is applied to all the phases andgenerated by a comparison of a control voltage signal PWM of a phase oran inner voltage signal COMP of the converter with a control signalRAMPA_BOOST, with this control signal RAMPA_BOOST being brought to adetermined voltage value, in particular corresponding to a value of aninner voltage reference of the converter, for example a supply voltagereference Vdd, in correspondence with the detection impulse signalLTPULSE.

Finally, in the illustrative embodiment the step of recovering theinterleaving driving phase shift provides a comparison step of the ORtype between the turn-off control signal LowsideOff and the drivingsignal PWM of each phase, with the recovery of the normal operation ofthe converter occurring in an automatic way once the turn-off controlsignal is ended.

This method for controlling a converter of the multiphase interleavingtype is realized by a controller according to one embodiment of thepresent invention, as shown in FIG. 5.

The controller 30 comprises a Load Transient detector 32 having an inputterminal FD connected, by a network 31 comprising the series of acapacitor Cd and a resistor Rd, to an OUT terminal of the converter ofthe multiphase interleaving type for the connection for example with aCPU.

The Load Transient detector 32 has an output terminal LT_COMP connectedto a flip-flop 34, having in turn an input terminal connected to aninner voltage reference LT_REF and an output terminal suitable forsupplying a switch 36 with a detection signal LTPULSE. By way ofillustration, hereafter reference will be made to the signals and to theterminals where these signals are present by using the same references.

The switch 36 is inserted between a supply voltage reference Vdd and anoscillator 37, which is suitable for supplying a current signal Iosc/2,and has an output terminal RAMPA_BOOST that is connected to a firstinput terminal, in particular an inverting one, of an output comparator.The output comparator has a second input terminal, in particular anon-inverting one, that receives a signal COMP, which corresponding tothe signal at the homonymous inner terminal of the multiphaseinterleaving converter, as described above, and an output terminalLowsideOff.

The controller 30 also comprises a regulation circuit 35 that isconnected to the Load Transient detector 32, in particular to theterminal LT_COMP, and to the flip-flop 34.

In particular, as shown in FIG. 6, the Load Transient detector 32comprises an input amplifier A1, in particular an operational amplifier,connected to ground GND, having a first input terminal, in particular anon-inverting one, connected to the inner voltage reference LT_REF, asecond input terminal, in particular an inverting one, connected to theterminal FD and thus, through the network 31, to the terminal OUT, aswell as an output terminal, LT_INFO feedback connected to the secondinput terminal through a resistor R1.

The Load Transient detector 32 also comprises an output amplifier A2, inparticular a threshold comparator, having a first input terminal, inparticular a non-inverting one, connected to the output terminal LT_INFOof the input amplifier A1, a second input terminal, in particular aninverting one, connected to a voltage reference equal to the innervoltage reference LT_REF summed with a “neat” triggering voltage Vref ofthe threshold comparator A2, as well as an output terminal, LT_COMP.

In substance, the Load Transient detector 32 is a threshold derivingcircuit in which the input amplifier A1 detects the derivative of thevoltage signal Vout at the terminal OUT of the controller 30 through thenetwork 31 comprising the resistor Rd and the capacitor Cd connected tothe terminal FD, with the value of the inner voltage reference LT_REFdetermining the triggering of the output amplifier A2 in correspondencewith the detection of the positive derivative of the voltage signalVout.

It is also possible to introduce, into the Load Transient detector 32,two output amplifiers having respective input terminals connected toinner voltage references chosen so as to cause their triggering on thedetection of the positive, and respectively negative, derivative of thevoltage signal Vout.

A preferred embodiment of the controller 30 is shown in greater detailin FIG. 7.

As already seen, the controller 30 has a connection terminal OUT, forexample for a CPU, connected, by the network 31 composed of thecapacitor Cd and the resistor Rd, to the terminal FD, which is in turnconnected to the Load Transient detector 32.

In particular, the Load Transient detector 32 comprises the amplifier Alhaving a first input terminal, a non-inverting one, connected, by aresistor R2 to a first generator G1 of the inner voltage referenceLT_REF, a second input terminal, an inverting one, connected to theterminal FD, and an output terminal. The first generator G1 is connectedbetween a first input terminal D of the flip-flop 34 and a first inputterminal, an inverting one, of the comparator A2, which has a secondinput terminal, a non-inverting one, connected to the output terminal ofthe amplifier A1 and an output terminal suitable for supplying a signalLT_COMP to a second input terminal CP of the flip-flop 34, as well as tothe regulation circuit 35. In particular, the first input terminal ofthe comparator A2 receives a voltage value equal to the sum of the innervoltage reference LT_REF and a triggering voltage Vref equal to G1*R2.

In substance, the value of the voltage supplied by the first generatorG1 determines the triggering threshold of the output amplifier A2 and asign change thereof allows this triggering to be performed upondetection of the positive, respectively negative, derivative of thevoltage signal Vout.

The regulation circuit 35 comprises a delay element DL inserted betweenthe output terminal of the comparator A2 and an inverter INV, which isin turn connected to a control terminal CD of the flip-flop 34, whichhas at least one output terminal Q suitable for supplying the switch 36with the detection impulse signal LTPULSE.

The switch 36 comprises a transistor M1 having a first conductionterminal connected to a supply voltage reference Vdd, a secondconduction terminal connected to a current generator G4, which is inturn connected to ground GND, and a control terminal connected to theoutput terminal Q of the flip-flop 34. Moreover, a capacitor Cboost isinserted in parallel to the current generator G4 between the secondconduction terminal of the transistor M1 and ground GND.

The interconnection point between the transistor M1 and the capacitorCboost is also connected to a first terminal, an inverting one, of theoutput comparator 38, which has a second input terminal that receivesthe signal COMP, as well as an output terminal suitable for supplyingthe turn-off control signal LowsideOff.

The transistor M1, the current generator G4 and the capacitor Cboostgenerate a control signal RAMPA_BOOST having the form indicated in thefigure, applied to the first input terminal of the output comparator 38.In particular, the control signal RAMPA_BOOST is brought to a valuecorresponding to the supply voltage in correspondence with a pulse ofthe impulse signal LTPULSE supplied by the flip-flop 34.

Advantageously according to this embodiment of the present invention, asdescribed above, the Load Transient detector 32 is only sensitive to thepositive derivative of the voltage signal Vout at the terminal OUT ofthe controller 30. In particular, when the comparator A2 triggersfurther to the detection of the derivative of the voltage signal Vout,the flip-flop 34 creates a detection impulse signal LTPULSE which closesthe switch 36, increasing in this way the control signal RAMPA_BOOST tothe supply voltage value Vdd.

Moreover, the detection impulse signal LTPULSE generated by theflip-flop 34 is regulated by the delay introduced by the delay elementDL of the regulation circuit 35.

As already seen in connection with the conventional controller, to notalso derive the residual ripple of the signal Vout (which is a signalwith frequency equal to N*Fsw), the network 31 is sized so as to respectthe following relation.

½πRd*Cd>j*Fsw

where Rd is the resistance value of the resistor Rd, Cd is the capacityvalue of the capacitor Cd, and N*Fsw is the frequency of the Voutsignal.

The ripple of the output voltage signal Vout is about 10 mVpeak-to-peak, while the voltage drop DVout further to a Load Transientis about 100 mV. Moreover, in the case of a Load Transient, it is soquick as to consider the impedance associated with the capacitor Cd ofthe network 31 almost void. Thus, considering that the current value Idflowing through the resistor Rd is equal to Id=DVout/Rd, it is possibleto size the resistor Rd so that the following relation occurs.

DVout/Rd×Rdd>Vref

where Rdd is the resistance value of the feedback resistor, and Vref isthe “neat” triggering voltage value of the comparator A2 (equal toG1*R2, with reference to FIG. 7).

Thus it is obtained that the resistance value of the resistor Rd mustrespect the following relation.

Rd<DVout×Rdd/Vref

In substance, the detection impulse signal LTPULSE is generated by theflip-flop 34 in the case of a quick load decrease; the controller 30realizing in this way the step of detecting the Load Transient, inparticular of the load release.

In fact, when the comparator A2 of the Load Transient detector 32triggers further to the detection of the positive derivative of theoutput voltage signal Vout, the flip flop 32 generates an impulse signalLTPULSE as small as desired, regulated by the delay element DL of theregulation circuit 35. This impulse signal LTPULSE, which is applied tothe control terminal of the switch 36, closes the switch and forces thesignal RAMPA_BOOST to rise to the supply voltage value Vdd.

Advantageously according to this embodiment of the present invention,the turn-off control signal LowsideOff turns off all the Low Sideswitches in the phases of the converter connected to the controller 30.In this way, the controller 30 exploits the body-brake technique at thedetection of a sudden load decrease (i.e., at the detection of thepositive derivative of the output voltage Vout).

The turn-off control signal LowsideOff is generated for a time intervalcorresponding to the following condition:

RAMPA_BOOST>COMP

imposed by the output comparator 38 which receives these signals on itsinput terminals, as shown in FIGS. 8A-8C that illustrate the patterns ofthe current signals IL of the inductances of the phases (FIG. 8A), thevoltage values inside the controller 30 (FIG. 8B), and the pattern ofthe output voltage signal Vout (FIG. 8C).

In particular, further to the generation of the detection impulse signalLTPULSE, the voltage across the capacitor Cboost (suitably chosen withvalues equal to a capacitance Cosc used for generating the triangularramps of the control voltage signals PWM of the phases of the converterconnected to the controller 30) is brought to the reference voltagevalue. The output comparator 38 thus generates a turn-off control signalLowsideOff of the impulse type, comparing the control voltage signal PWMof a phase or the voltage signal COMP applied to its second inputterminal with the control signal RAMPA_BOOST applied to its first inputterminal. The duration of the turn-off control signal LowsideOff dependson the controller 30, i.e., on the control voltage, which, during anegative Load Transient, i.e., in correspondence with a load release,tends to decrease. In fact, the turn-off control signal LowsideOff isthe signal of the output terminal of the comparator 38; this comparator38 compares the control signal RAMPA_BOOST with the voltage signal COMP,which is in turn the signal of the output terminal of the controller,i.e., the value of the control voltage. This control voltage issubstantially a signal carrying the information about the amount ofenergy to be transferred from the input terminal to the output terminalof the converter. The dependency of the duration of the turn-off controlsignal LowsideOff from the control voltage thus allows control of theenergy transferred by the converter.

The turn-off control signal LowsideOff generated by the controller 30 isused to simultaneously turn off the High Side and Low Side switches ofall the phases of the converter connected to the controller 30,cancelling the interleaving phase shift of the driving of these phasesand using the body-brake technique, in particular through a plurality ofsignals PWM_COMP generated by an OR driving architecture 40, as shown inFIG. 9.

The driving architecture 40 shown in FIG. 9 relates, as a non-limitingexample, to the case of four phases for which it generates four drivingsignals, PWM_COMP<1> to PWM_COMP<4>. It comprises a plurality, in thisillustrative example four, of driving sub-systems 41, each comprising athreshold comparator TC having a first input terminal, an inverting one,receiving a ramp signal RAMPA of the relative phase, a second inputterminal, a non-inverting one, receiving a control voltage signalVCONTROLLO and an output terminal suitable for supplying a first inputterminal A of a logic gate LG of the OR type with a signal PWM. Thelogic gate has a second input terminal B that receives the turn-offcontrol signal LowsideOff and an output terminal Y suitable forsupplying the real turn-off control signal LowsideOff_COMP.

In this way, the simultaneous turn-off of the phases occurs by realizingan Or of the signals PWM and the turn-off control signal LowsideOffthanks to the driving architecture 40.

Considering that the ramp signals (RAMPA1 to RAMPA4) are constructed bycharging and discharging a capacitance Cosc with a current Iosc, thenthe control signal RAMPA_BOOST is advantageously created with a slopeequal to half the isosceles-triangle-shaped ramps of the driving signalsPWM. In particular, the ramp signals RAMPA1 to RAMPA4 areisosceles-triangle-shaped ramps which, compared with the control voltagesignals VCONTROLLO1 to VCONTROLLO4 create driving signals of the PWMtype by the comparators TC1 to TC4.

Advantageously according to this embodiment of the present invention,the controller 30 thus comprises a capacitor Cboost with a capacitancevalue equal to Cosc and current generator G4 of the oscillator 37supplies a discharge current equal to Iosc/2.

The fact that the slope of the control signal RAMPA_BOOST is chosen tobe equal to half the ramps of the driving signals PWM ensures continuityin the control action of the controller 30. All this is mathematicallyequivalent to a non-varying loop gain of the overall system comprisingthe controller 30 and the corresponding converter.

At this point, the recovery of the interleaving phase shift is to beprovided for the driving of the phases during the normal operation ofthe converter.

Advantageously, by using the controller 30 according to this embodimentof the present invention the recovery of the interleaving phase shift isautomatic since it has never been interrupted. In particular, when theturn-off control signal LowsideOff ends, the phases of the converterstart to work again following the interleaving phase shift of thedriving signals PWM.

Accordingly, the controller 30, after having detected a Load Transient,in particular a load release, through the Load Transient detector 32that is sensitive to the positive derivative of the output voltagesignal Vout, brings the control signal RAMPA BOOST to the supply voltagevalue Vdd and compares it with any control voltage, generating aturn-off control signal LowsideOff of the impulse type which “resets”the driving signals PWM thanks to the OR driving architecture 40. Inthis way, in response to a Load Transient, all the phases are turned offby the turn-off control signal LowsideOff, reducing the current levelmade available for the load connected to the terminal OUT.

Advantageously, all the power transistors of the phases aresimultaneously turned off, both the High Side switches and the Low Sideswitches.

Moreover, advantageously the recovery of the interleaving driving isautomatic, once the Load Transient has ended and the control signalRAMPA_BOOST has gone down again, thanks to the driving architecture 40of the OR type.

While there has been illustrated and described what are presentlyconsidered to be the preferred embodiments of the present invention, itwill be understood by those skilled in the art that various othermodifications may be made, and equivalents may be substituted, withoutdeparting from the true scope of the present invention. Additionally,many modifications may be made to adapt a particular situation to theteachings of the present invention without departing from the centralinventive concept described herein. Furthermore, an embodiment of thepresent invention may not include all of the features described above.Therefore, it is intended that the present invention not be limited tothe particular embodiments disclosed, but that the invention include allembodiments falling within the scope of the appended claims.

What is claimed is:
 1. A method for controlling a converter of themultiphase interleaving type, the converter including a plurality ofphases, the method comprising the steps of: detecting when a change of aload applied to an output terminal of the converter occurs; providing anoutput comparator having at least one input terminal receiving an innersignal of the converter, and an output terminal connected to the outputterminal of the controller for generating a turn-off control signal forthe phases of the converter; providing a switch having an outputterminal connected to at least one input terminal of the outputcomparator; providing an oscillator connected to the switch; in responseto the turn-off control signal, simultaneously turning off all of thephases of the converter; and recovering a driving interleaving phaseshift so as to restart a normal operation of the converter, wherein theswitch comprises a transistor coupled between a second voltage referenceand the oscillator.
 2. The method according to claim 1, wherein therecovering step comprises making an OR-type comparison between theturn-off control signal and the driving signals of the phases.
 3. Themethod according to claim 1, further comprising the step of providing aflip-flop having at least one output terminal connected to the switch.4. The method according to claim 3, wherein the transistor has a controlterminal connected to the flip-flop.
 5. The method according to claim 3,wherein the transistor has a first conduction terminal connected to thesecond voltage reference and a second conduction terminal connected to agenerator of the oscillator, and a control terminal connected to the atleast one output terminal of the flip-flop.
 6. The method according toclaim 5, wherein the oscillator further comprises a capacitor connectedin parallel to the generator, an interconnection point of the transistorand the capacitor being connected to the at least one input terminal ofthe output comparator.
 7. The method according to claim 6, wherein thecapacitor is sized as a capacitor used for generating ramp controlvoltage signals of the phases of the converter and the generatorsupplies a current value equal to half of a current value as used forgenerating the ramp control voltage signals.
 8. A controller for aconverter of the multiphase interleaving type, the converter including aplurality of phases, the controller comprising: at least one inputterminal connected to an output terminal of the converter; at least oneoutput terminal connected to all of the phases of the converter; atleast one load change detector detecting when a change of a load appliedto the output terminal of the converter; an output comparator having atleast one input terminal receiving an inner signal of the converter, andan output terminal connected to the output terminal of the controllerfor generating a turn-off control signal for the phases of theconverter, the turn-off control signal forcing the turn-off of thephases of the converter; a flip-flop having at least one outputterminal; a switch connected to the output terminal of the flip-flop,the switch having an output terminal connected to at least one inputterminal of the output comparator; and an oscillator connected to theswitch, wherein the switch comprises a transistor inserted between asecond voltage reference and the oscillator, the transistor having acontrol terminal connected to the flip-flop.
 9. The controller accordingto claim 8, wherein the transistor has a first conduction terminalconnected to the second voltage reference and a second conductionterminal connected to a generator of the oscillator, and a controlterminal connected to the at least one output terminal of the flip-flop.10. The controller according to claim 9, wherein the oscillator furthercomprises a capacitor connected in parallel to the generator, aninterconnection point of the transistor and the capacitor beingconnected to the at least one input terminal of the output comparator.11. The controller according to claim 10, wherein the capacitor is sizedas a capacitor used for generating ramp control voltage signals of thephases of the converter and the generator supplies a current value equalto half of a current value as used for generating the ramp controlvoltage signals.
 12. The controller according to claim 8, wherein thedetector comprises: an input amplifier having a first input terminalcoupled to the inner voltage reference, a second input terminal coupledto the input terminal of the controller, and an output terminal; and anoutput amplifier having a first input terminal connected to the outputterminal of the input amplifier.
 13. The controller according to claim12, wherein the second input terminal of the output amplifier receives avoltage value equal to the sum of the inner voltage reference and atriggering voltage of the output amplifier.
 14. The controller accordingto claim 12, wherein the generator is further connected to an inputterminal of the flip-flop, the flip-flop having another input terminalconnected to an output terminal of the output amplifier.
 15. Thecontroller according to claim 8, wherein the flip-flop generates on itsoutput terminal an impulse signal in correspondence with the load changedetected by the detector.
 16. A controller for a converter of themultiphase interleaving type, the converter including a plurality ofphases, the controller comprising: at least one input terminal connectedto an output terminal of the converter; at least one output terminalconnected to all of the phases of the converter; at least one loadchange detector detecting when a change of a load applied to the outputterminal of the converter; an output comparator having at least oneinput terminal receiving an inner signal of the converter, and an outputterminal connected to the output terminal of the controller forgenerating a turn-off control signal for the phases of the converter,the turn-off control signal forcing the turn-off of the phases of theconverter; and a driving architecture of the OR type comprising aplurality of driving sub-systems, each including at least one thresholdcomparator having a first input terminal receiving a ramp controlvoltage signal of a corresponding phase of the converter, a second inputterminal receiving a control voltage signal, and an output terminal forsupplying a first input terminal of an OR logic gate with a signal ofthe PWM type, the OR logic gate having a second input terminal receivingthe turn-off control signal and an output terminal for supplying adriving signal of the corresponding phase.
 17. The controller accordingto claim 16, further comprising: a flip-flop having at least one outputterminal, the flip-flop generating on its output terminal an impulsesignal in correspondence with the load change detected by the detector;and a switch connected to the output terminal of the flip-flop, theswitch having an output terminal connected to at least one inputterminal of the output comparator, wherein the switch generates acontrol signal which is brought to a determined voltage value incorrespondence with the impulse signal and is applied to the outputcomparator.
 18. The controller according to claim 17, wherein thecontrol signal generated by the switch is a ramp signal having a slopeequal to half of the ramp control voltage signals of the phases.